Solutions for the exercises found here.
NOTE: Perfectly valid solutions can be written in a different style than the solutions below. If your code works, it works! Don't feel like your functions need to have the exact same syntax as these solutions.
Table of Contents:
Summation to n: Let's implement the function sum that takes a single
parameter n, and computes the sum of all integers up to n starting from
0, e.g.:
function sum(n) {
var current = 0;
var sum = 0;
while (current <= n) {
sum = sum + current;
current = current + 1;
}
return sum;
}
sum(3); // => 6
sum(4); // => 10
sum(5); // => 15Factorial of n: The factorial of n is the product of all the
integers preceding n, starting with 1, e.g.:
function factorial(n) {
var current = 1;
var product = 1;
while (current < n) {
product = product * current;
current = current + 1;
}
return product;
}
factorial(3); // => 6
factorial(4); // => 24
factorial(5); // => 120Repeating a String n Times: Let's write a function called
repeatString that takes two parameters: a string str, which is the string
to be repeated, and count -- a number representing how many times the
string s should be repeated, e.g.
function repeatString(str, count) {
var finalString = '';
var start = 0;
while (start < count) {
finalString = finalString + str;
start = start + 1;
}
return finalString;
}
repeatString('dog', 0); // => ''
repeatString('dog', 1); // => 'dog'
repeatString('dog', 2); // => 'dogdog'
repeatString('dog', 3); // => 'dogdogdog'Your task is to implement the repeatString function using a while loop.
Modify your sum function from the Basic Requirements section to accept
two parameters, start and end: sum should now compute the sum of the
numbers from start to end, e.g.
function sum(start, end) {
var current = start;
var sum = 0;
while (current <= end) {
sum = sum + current;
current = current + 1;
}
return sum;
}
sum(2, 7); // => 2 + 3 + 4 + 5 + 6 + 7 => 27
sum(3, 5); // => 3 + 4 + 5 => 12start is larger than end? Modify sum to check for this
case and, when found, swap the start and end arguments.function sum(start, end) {
var current = start;
var sum = 0;
if (start > end) {
current = end;
end = start;
}
while (current <= end) {
sum = sum + current;
current = current + 1;
}
return sum;
}
sum(2, 7); // => 2 + 3 + 4 + 5 + 6 + 7 => 27
sum(3, 5); // => 3 + 4 + 5 => 12Let's pretend for a moment that JavaScript does not have the addition
operator + -- instead, it comes with two functions called inc and dec
that perform increment and decrement respectively:
// ignore the fact that inc makes use of +
function inc(x) {
return x + 1;
}
function dec(x) {
return x - 1;
}Your task is to write a function called add that takes two numbers as
parameters, x and y, and adds them together. The catch is that you can
only use inc and dec to accomplish this.
function add(x, y) {
var sum = x;
while (y > 0) {
sum = inc(sum);
y = dec(y);
}
return sum;
}Write a function called isEven that, given a number n as a parameter,
returns true if that number is even, and false otherwise; however, you
need to do this without using the % operator.
function isEven(n) {
while (n > 0) {
n = n - 2;
}
if (n === 0) {
return true;
}
return false;
}Write a function called multiply that accepts two numbers as parameters,
and multiplies them together -- but without using the * operator; instead,
you'll need to use repeated addition.
function multiply(x, y) {
var product = 0;
while (y > 0) {
product = product + x;
y = y - 1;
}
return product;
}Compute the nth Fibonacci Number: The fibonacci numbers are represented by the
following sequence:
// fib(n): 1 1 2 3 5 8 13 21
// | | | | | | | |
// n: 0 1 2 3 4 5 6 7That is, fib(0) is 1, fib(1) is 1, fib(2) is 2, fib(3) is 3, fib(4)
is 5, etc.
Notice that each fibonacci number can be computed by adding the previous
two fibonacci numbers, with the exception of the first two: fib(0) and
fib(1). More succinctly,
fib(0) is 1fib(1) is 1fib(n) is fib(n - 1) + fib(n - 2)Write a function called fib that accepts a number n as a parameter and
computes the nth fibonacci number using the above rules.
// Using a for loop
function fibF(n) {
var result = [1, 1];
for (let i = 2; i <= n; i++) {
const a = result[i - 1];
const b = result[i - 2];
result.push(a + b);
}
return result[n];
}
// Using recursion (function calls itself)
function fibR(n) {
if (n < 2) {
return 1;
}
return fibR(n - 1) + fibR(n - 2);
}By now you should have worked with the length property of strings, e.g.
"hello".length. Your task is to write a function called stringLength that
accepts a string as a parameter and computes the length of that string;
however, as you may have guessed, you are not allowed to use the length
property of the string!
Instead, you'll need to make use of the string method called slice. To
get an idea of how slice works, try the following at a console:
"hello".slice(0);
"hello".slice(1);
"".slice(1);For our purposes, we can consider slice as taking one argument -- the
index to begin slicing from, and returns a new string starting from that
index onwards.
Indices are positions of characters within strings, and they always begin counting from 0, e.g.:
// "h e l l o" (spaces added for clarity)
// | | | | |
// 0 1 2 3 4The "h" character has index (position) 0 in the string "hello", "e"
has index 1, l has index 2, etc.
function stringLength(str) {
var length = 0;
while (str !== '') {
length = length + 1;
str = str.slice(1);
}
return length;
}The "modulo" operator (%) computes the remainder after dividing its left
operand by its right one, e.g.
5 % 2; // => 1
8 % 10; // => 8
7 % 5; // => 2Write a function called modulo that works like the % operator, but
without using it.
function modulo(x, y) {
var dividedFloor = Math.floor(x / y);
var productInteger = dividedFloor * y;
var remainder = x - productInteger;
return remainder;
}Write a function called countChars that accepts two parameters: a string
and a character. This function should return a number representing the
number of times that the character appears in string. To access the
first element of a string, you can use the following syntax:
// access the element at index 0
"hello"[0]; // => "h"
"dog"[0]; // => "d"HINT: You'll also need to make use of the slice method as shown above
in the exercise on computing the length of a string.
function countChars(str, char) {
var count = 0;
while (str.length > 0) {
if (str[0] === char) {
count = count + 1;
}
str = str.slice(1);
}
return count;
}Implement a function called indexOf that accepts two paramters: a string
and a character, and returns the first index of character in the
string. You'll need to make use of the techniques for accessing the first
element of a string and the rest of the string (slice) as before.
function indexOf(str, char) {
var index = 0;
while (str.length) {
if (str[0] === char) {
return index;
}
index = index + 1;
str = str.slice(1);
}
// If the character is not found in the string, return -1 to indicate
return -1;
}Using the array: ["cat", "fox", "dog", "monkey"], what is the index of:
Fix the syntax/style in the following arrays:
[ 1, 3 4 7,9, ]
"the""quick""brown","fox" "jumped","over" the lazy, "dog", ]
[true false,trueFIXED:
[1, 3, 4, 7, 9]
["the", "quick", "brown", "fox", "jumped", "over", "the", "lazy", "dog"]
[true, false, true]Create arrays in the global scope of your program consisting of strings that represent:
Using the arrays that you created in the last exercise, use the console to access:
Write a function first that takes an array as an argument and returns the
first element in that array.
function first(arr) {
return arr[0];
}Write a function last that takes an array as an argument and returns the
last element in the array. Hint: What is the relationship between the
index of the last element in the array and the length of the array?
function last(arr) {
var lastIndex = arr.length - 1;
return arr[lastIndex];
}Using push and unshift, make this array contain the
numbers from zero through seven:
var arr = [2, 3, 4];
arr.unshift(1);
arr.unshift(0);
arr.push(5);
arr.push(6);
arr.push(7);
arr; // => [0, 1, 2, 3, 4, 5, 6, 7]What is returned by push? Before throwing this into the console, form a
hypothesis about what you think the return value will be:
var arr = [5, 7, 9];
arr.push(6); // => ???Were you correct? What is the returned by push? Does unshift work in the
same way?
ANSWER: Both .push() and .unshift() return the length of the new array.
We can use the assignment operator (=) to replace elements in arrays with
other ones like so:
var animals = ['dog', 'elephant', 'zebra']
// let's replace 'dog' with 'hippo'
animals[0] = 'hippo';
animals; // => ['hippo', 'elephant', 'zebra']Using the same principle, perform the following:
// 1. Change all odd numbers to be those numbers multiplied by two:
var numbers = [4, 9, 7, 2, 1, 8];
numbers[1] = numbers[1] * 2;
numbers[2] = numbers[2] * 2;
numbers[4] = numbers[4] * 2;
numbers; // => [4, 18, 14, 2, 2, 8]
// 2. Fix the typos by replacing each element with a correctly spelled version
var places = ['snfranisco', 'oacklannd', 'santacrus']
places[0] = 'san francisco';
places[1] = 'oakland';
places[2] = 'santa cruz';
places; // => ['san francisco', 'oakland', 'santa cruz']Write a function called nth that accepts an array and an index as
parameters, and returns the element at that index.
function nth(array, index) {
return array[index];
}
var animals = ['dog', 'cat', 'gerbil'];
nth(animals, 2); // => 'gerbil'
nth(animals, 1) === animals[1]; // => trueWrite a function rest that returns all the elements in the array except
for the first one. HINT: Read about the slice method on
MDN
and/or experiment with slice at the console like so:
var numbers = [3, 2, 7, 5];
numbers.slice(0);
numbers.slice(1);
numbers.slice(2);
numbers.slice(0, 2);function rest(arr) {
return arr.slice(1);
}Write a function butlast that returns all of the elements in the array
except for the last one (you may want to use slice for this one as well).
function butlast(arr) {
return arr.slice(0, -1);
}Complete the function cons that accepts an element and an array, and
returns an array with the element added to the front of the array:
function cons(x, array) {
array.unshift(x);
return array;
}Complete the function conj that accepts an array and an element, and
returns an array with the element added to the end of the array:
function conj(array, x) {
array.push(x);
return array;
}What benefit(s) might there be to using functions like cons or conj over
unshift or push?
ANSWER: The array that we are modifying is being returned to us when we use these functions, whereas .unshift() and .push() return the array's new length. It is often the case that we want to perform addition operations using the array after it has been modified; using these functions makes doing so easier.
Try the following in a console:
var arr = [];
arr[7] = "Hello."
arr; // => ???What is the value of arr after assigning an element to its seventh index?
Explain the result in plain English.
ANSWER:
The value of arr is an array with the following characteristics:
"Hello." as its 8th element (index 7)
In order to assign a value at index 7 (arr[7] = "Hello.") JavaScript has inserted empty elements at all preceding indices. It may help to think of arrays like a collection of boxes in which we can store values, with each box representing an element at a given index. In order to have a value in our 8th box (arr[7]), we must have the other boxes that came before it, even if they are empty.Without running the below function, use a whiteboard to figure out what it should return by repeatedly expanding function invocations:
function mystery(array) {
if (array.length === 0) {
return [];
}
return conj(mystery(rest(array)), first(array));
}Using first, rest, conj and/or cons, write functions that accomplish
the following:
function first(arr) {
return arr[0];
}
function rest(arr) {
return arr.slice(1);
}
function cons(x, array) {
array.unshift(x);
return array;
}
function conj(array, x) {
array.push(x);
return array;
}sum all the elements of an arrayfunction sumArray(arr) {
var sum = 0;
while (arr.length > 0) {
sum = sum + first(arr);
arr = rest(arr);
}
return sum;
}function squaredArray(arr) {
var squaredArr = [];
while (arr.length > 0) {
var squaredNum = first(arr) * first(arr);
conj(squaredArr, squaredNum);
arr = rest(arr);
}
return squaredArr;
}function evenArray(arr) {
var evenArr = [];
while (arr.length > 0) {
var current = first(arr);
if (current % 2 === 0) {
conj(evenArr, current);
}
arr = rest(arr);
}
return evenArr;
}HINT: After figuring out how the mystery function works above, use it
as a reference for how to write this type of function.
Before getting started, make sure that you have a JavaScript console open (like repl.it), so you can complete these exercises.
Try to write all of the exercises using both the for loop and while
loop.
sum that computes the sum of the numbers in an array.function sumFor(nums) {
var total = 0;
for (var i = 0; i < nums.length; i = i + 1) {
total = total + nums[i];
}
return total;
}
function sumWhile(nums) {
var total = 0;
var i = 0;
while (i < nums.length) {
total = total + nums[i];
i = i + 1;
}
return total;
}max that accepts an array of numbers and returns the
largest number in the array.function maxFor(nums) {
var largest = nums[0];
for (var i = 0; i < nums.length; i = i + 1) {
if (nums[i] > largest) {
largest = nums[i];
}
}
return largest;
}
function maxWhile(nums) {
var largest = nums[0];
var i = 0;
while (i < nums.length) {
if (nums[i] > largest) {
largest = nums[i];
}
i = i + 1;
}
return largest;
}"the quick brown fox jumped over the lazy dog".split(" ");
"Hello, world!".split("")
"1,2,3,4,5,6".split(",")What is returned by split (You can read more about it
here),
and how does it work?
ANSWER: The split() method splits a string into an array of strings by separating the string into substrings, using a specified separator string to determine where to make each split. This separator string is the argument passed to .split(). The return value is the array of substrings.
Use split to write a function longestWord that takes a string as an
argument and returns the longest word.
function longestWordFor(str) {
var split = str.split(' ');
var longest = split[0];
for (var i = 0; i < split.length; i = i + 1) {
if (split[i].length > longest.length) {
longest = split[i];
}
}
return longest;
}
longestWordFor('all your base are belong to us') // => 'belong';
function longestWordWhile(str) {
var split = str.split(' ');
var longest = split[0];
var i = 0;
while (i < split.length) {
if (split[i].length > longest.length) {
longest = split[i];
}
i = i + 1;
}
return longest;
}
longestWordWhile('all your base are belong to us') // => 'belong';remove that accepts an array and an element, and
returns an array with all ocurrences of element removed.function removeFor(array, element) {
var removed = [];
for (var i = 0; i < array.length; i = i + 1) {
if (array[i] !== element) {
removed.push(array[i]);
}
}
return removed;
}
removeFor([1, 3, 6, 2, 3], 3); // => [1, 6, 2]
function removeWhile(array, element) {
var removed = [];
var i = 0;
while (i < array.length) {
if (array[i] !== element) {
removed.push(array[i]);
}
i = i + 1;
}
return removed;
}
removeWhile([1, 3, 6, 2, 3], 3); // => [1, 6, 2]evens that accepts an array as an argument, and returns
an array consisting of all of the even numbers in that array.function evensFor(array) {
var evenNums = [];
for (var i = 0; i < array.length; i = i + 1) {
if (array[i] % 2 === 0) {
evenNums.push(array[i]);
}
}
return evenNums;
}
evensFor([1, 2, 3, 4, 5, 6, 7, 8]) // => [2, 4, 6, 8];
function evensWhile(array) {
var evenNums = [];
var i = 0;
while (i < array.length) {
if (array[i] % 2 === 0) {
evenNums.push(array[i]);
}
i = i + 1;
}
return evenNums;
}
evensWhile([1, 2, 3, 4, 5, 6, 7, 8]) // => [2, 4, 6, 8];average that takes an array of numbers as a
parameter and returns the average of those numbers.function averageFor(array) {
var result = 0;
for (var i = 0; i < array.length; i = i + 1) {
result = result + array[i];
}
return result / array.length;
}
averageFor([1, 2, 3, 4, 5]) // => 3;
function averageWhile(array) {
var result = 0;
var i = 0;
while (i < array.length) {
result = result + array[i];
i = i + 1;
}
return result / array.length;
}
averageWhile([1, 2, 3, 4, 5]) // => 3;min that finds the smallest number in an array of
numbers.function minFor(array) {
var min = array[0];
for (var i = 0; i < array.length; i++) {
if (array[i] < min) {
min = array[i];
}
}
return min;
}
minFor([10, 12, 5, 15, 20]) // => 5;
function minWhile(array) {
var min = array[0];
var i = 0;
while (i < array.length) {
if (array[i] < min) {
min = array[i];
}
i = i + 1;
}
return min;
}
minWhile([10, 12, 5, 15, 20]) // => 5;shortestWord that works like longestWord, but returns
the shortest word instead.function shortestWordFor(str) {
var split = str.split(' ');
var shortest = split[0];
for (var i = 0; i < split.length; i = i + 1) {
if (split[i].length < shortest.length) {
shortest = split[i];
}
}
return shortest;
}
shortestWordFor('all your base are belong to us') // => 'to';
function shortestWordWhile(str) {
var split = str.split(' ');
var shortest = split[0];
var i = 0;
while (i < split.length) {
if (split[i].length < shortest.length) {
shortest = split[i];
}
i = i + 1;
}
return shortest;
}
shortestWordWhile('all your base are belong to us') // => 'to';countChar that takes two arguments: any string, and a
character (string of one letter), and returns the number of times that the
character occurs in the string.function countCharFor(str, char) {
var occurances = 0;
for (var i = 0; i < str.length; i = i + 1) {
if (str[i] === char) {
occurances = occurances + 1;
}
}
return occurances;
}
countCharFor('hello world', 'o') // => 2;
function countCharWhile(str, char) {
var occurances = 0;
var i = 0;
while (i < str.length) {
if (str[i] === char) {
occurances = occurances + 1;
}
i = i + 1;
}
return occurances;
}
countCharWhile('hello world', 'o') // => 2;evenLengthWords that takes an array of strings as an
argument, and returns an array of just the words that have an even length.function evenLengthWordsFor(strings) {
var result = [];
for (var i = 0; i < strings.length; i = i + 1) {
if (strings[i].length % 2 === 0) {
result.push(strings[i]);
}
}
return result;
}
evenLengthWordsFor(['hello', 'world', 'I', 'am', 'here']) // => ['am', 'here'];
function evenLengthWordsWhile(strings) {
var result = [];
var i = 0;
while (i < strings.length) {
if (strings[i].length % 2 === 0) {
result.push(strings[i]);
}
i = i + 1;
}
return result;
}
evenLengthWordsWhile(['hello', 'world', 'I', 'am', 'here']) // => ['am', 'here'];join method on
MDN
and use it to implement a function that accepts a string as an argument and
returns that string reversed.function reverseString(str) {
return str.split('').reverse().join('');
}
reverseString('hello') // => 'olleh';keep that "keeps" certain elements in an array. The
function will need to take two arguments, an array, and something else --
the second argument will be what is used to determine which elements to keep.function keep(array, fn) {
var result = [];
for (var i = 0; i < array.length; i = i + 1) {
if (fn(array[i]) === true) {
result.push(array[i]);
}
}
return result;
}You should be able to use this function to write evens, evenLengthWords,
a hypothetical odds function, or oddLengthWords without changing the
keep function.
Fix the syntax & style issues with the three objects below:
{firstName "Josh", lastname: "Lehman" }
{a: 1, b:2 c: 3 d 4}
{
animal: "dog"
noise: "bark",
age: 3,
type "Labrador"
color: "Yellow",
}FIXED:
{
firstName: "Josh",
lastName: "Lehman"
}
{
a: 1,
b: 2,
c: 3,
d: 4
}
{
animal: "dog",
noise: "bark",
age: 3,
type: "Labrador",
color: "Yellow";
}{
firstName: "Michael",
lastName: "Jordan",
age: 56,
hometown: "Wilmington, NC"
}Add three more key/value pairs to your object that represent other attributes of yourself. Ideas include (but are not limited to):
HINT: You can just modify the object that you created before.
{
firstName: "Michael",
lastName: "Jordan",
age: 56,
hometown: "Wilmington, NC",
occupation: "NBA Owner",
dateOfBirth: "February 17, 1963",
nbaTitles: 6
}The values in an object can be objects themselves, and in fact, this is a very common pattern. For example, consider the following object that represents a computer:
var computer = {
brand: "Apple",
year: 2014,
model: "MacBook Pro",
size: "15-inch",
specs: {
processor: "2.3GHz Intel Core i7",
memory: "16 GB 1600 MHz DDR3",
graphics: "Intel Iris Pro 1536 MB"
}
}You should notice that the specs key in the computer object is an object
itself! We could access information about the processor using dot-notation
like so:
computer.specs.processor; // => "2.3GHz Intel Core i7"Change your object to have a name key, the value of which is an object
– this object should have first, last and middle keys
containing your first, last, and middle names respectively (make sure to
remove the firstName and lastName keys that you added before). You
should be able to access your last name afterwards like so (assuming your
object is called you):
var you = {
name: {
first: "Michael",
middle: "Jeffrey",
last: "Jordan"
},
age: 56,
hometown: "Wilmington, NC",
occupation: "NBA Owner",
dateOfBirth: "February 17, 1963",
nbaTitles: 6
};
you.name.last; // => YOUR LAST NAMELook up your favorite movie on IMDB, and make an object that represents some aspects of that movie, e.g.:
HINT: Most movies have multiple actors. What data-structure do we use to represent a collection of similar things?
var favMovie = {
title: "The Shawshank Redemption",
director: {
firstName: "Frank",
lastName: "Darabont"
},
yearReleased: 1994,
rating: 9.3,
actors: ["Tim Robbins", "Morgan Freeman", "Bob Gunton"]
};Perform these exercises in a console!
Create a new empty object in your console called obj like this:
var obj = {};Add a new key/value pair to the object obj by assigning a new value to a
new key like so:
obj.hello = "world";
obj["number"] = 25;Now, check the value of obj in the console and ensure that it has the two
key/value pairs added above. This is how we create new key/value pairs in
existing objects.
In the console, add a favoriteColor
key/value pair to the object that represents you.
obj.favoriteColor = "Blue";Fix the attempts to access values in the person object:
var key = "name";
var person = {
name: "Alyssa P. Hacker",
age: 26,
hometown: "somewhere"
};
person[age]; // => 26
person.key; // => "Alyssa P. Hacker"FIXED
person["age"]; // => 26
person.name; // => "Alyssa P. Hacker"Write a function fullName that takes a person object as an argument, and
returns that person's full name as a string. By person object, we mean an
object that has the structure of the object you created to represent
yourself above, for example:
var alyssa = {
name: {
first: "Alyssa",
middle: "P.",
last: "Hacker"
},
age: 26
};
function fullName(person) {
return person.name.first + " " + person.name.middle + " " + person.name.last;
}
fullName(alyssa); // => "Alyssa P. Hacker"What happens if you pass a person object to fullName that doesn't have a
middle name?
fullName({name: {first: "John", last: "Doe"}}); // => "John Doe"Your fullName function should work correctly regardless of whether or not
the person has a middle name -- if it doesn't produce the output shown above
when given the object {name: {first: "John", last: "Doe"}}, fix it so that
it does.
function fullName(person) {
if (person.name.middle) {
return person.name.first + " " + person.name.middle + " " + person.name.last;
}
return person.name.first + " " + person.name.last;
}We often deal with arrays of objects; below is an example of an array of objects, where each object represents a person:
var people = [
{name: {first: "Alyssa", middle: "P.", last: "Hacker"}, age: 26},
{name: {first: "Ben", last: "Bitdiddle"}, age: 34},
{name: {first: "Eva", middle: "Lu", last: "Ator"}, age: 40},
{name: {first: "Lem", middle: "E.", last: "Tweakit"}, age: 45},
{name: {first: "Louis", last: "Reasoner"}, age: 21}
];name key does not have the same "shape" as the ones above, make sure you
change it to look like these).fullName function here?function allFullNames(people) {
var result = [];
for (var i = 0; i < people.length; i = i + 1) {
var name = fullName(people[i]);
result.push(name);
}
return result;
}people array.function averageAge(people) {
var totalAges = 0;
for (var i = 0; i < people.length; i = i + 1) {
totalAges = totalAges + people[i].age;
}
return totalAges / people.length;
}function olderThan(people, age) {
var result = [];
for (var i = 0; i < people.length; i = i + 1) {
if (people[i].age > age) {
result.push(people[i]);
}
}
return result;
}The following object has a number of key/value pairs that need to be removed:
var dirtyObject = {
_fht: 192492,
name: "Alyssa P. Hacker",
age: 26,
_byz: 939205,
_ttrs: 510852
}
function clean(obj) {
// ...
}
clean(dirtyObject); // => {name: "Alyssa P. Hacker", age: 26}The function clean should accept an object as an argument and return a new
object that has all of the key/value pairs of its parameter except for those
that begin with _.
Write a function removeOddValues that takes an object as an argument and
returns an object with all key/value pairs removed for which the value holds
an odd number. You'll need to use the `typeof` operator to first check that
the values are numbers:
typeof "Hello"
typeof 3Look around at various physical objects in the room, or think about activities that you enjoy. How would you represent this things as objects? Practice creating objects to represent different things. Some ideas include:
Write a function countWords that, when given a string as an argument,
returns an object where keys are the words in the string, and values
are the number of occurrences of that word within the string:
function countWords(s) {
// ...
}
countWords("hello hello"); // => {"hello": 2}
countWords("Hello hello"); // => {"Hello": 1, "hello": 1}
countWords("The quick brown"); // => {"The": 1, "quick": 1, "brown": 1}HINT: You will want to make use of the string method split. Try
\"Hello hello".split(" ") at a console to see how it works.
countWords to be case insensitive by using the following string
method (experiment at a console with it to learn its behavior):"HElLo".toLowerCase(); // => ???Write a function countCharacters that, when given a string as an argument,
returns an object containing counts of the ocurrences of each character in
the string.
function countCharacters(s) {
// ...
}
countCharacters("hello"); // => {"h": 1, "e": 1, "l": 2, "o": 1}HINT: You will want to make use of the string method split. Try
\"hello".split("") at a console to see how it works.
Write a function select that accepts two arguments: an object and an
array. The array should contain names of keys that will be selected from
the object:
function select(obj, keys) {
// ...
}
select({a: 1, b: 2, c: 3}, ["a"]); // => {a: 1}
select({a: 1, b: 2, c: 3}, ["a", "c"]); // => {a: 1, c: 3}
select({a: 1, b: 2, c: 3}, ["a", "c", "d"]); // => {a: 1, c: 3}Write a function extends that accepts two objects as arguments, and
extends all of the key/value pairs of the second one to the first one.
function extend(obj1, obj2) {
// ...
}
extend({a: 1}, {b: 2}); // => {a: 1, b: 2}
extend({a: 1, c: 3}, {b: 2, c: 4}); // => {a: 1, b: 2, c: 4}The function Object.keys returns an array of an object's keys. Experiment
with it at the console like this:
Object.keys({a: 1, b: 2});Using this property, write versions of the above functions using repetition through function invocation (i.e. recursion)
The function JSON.stringify turns arbitrary JavaScript data structures
(arrays and objects) into strings. Try it out in a console like this:
JSON.stringify({a: 1, b: 2, c: ["dog", "cat", "zebra"], d: true});
JSON.stringify([5, 7, 2, 4, 0, 20]);
var people = [
{name: {first: "Alyssa", middle: "P.", last: "Hacker"}, age: 26},
{name: {first: "Ben", last: "Bitdiddle"}, age: 34},
{name: {first: "Eva", middle: "Lu", last: "Ator"}, age: 40},
{name: {first: "Lem", middle: "E.", last: "Tweakit"}, age: 45},
{name: {first: "Louis", last: "Reasoner"}, age: 21}
];
JSON.stringify(people);Write a function stringify that works exactly like JSON.stringify.
HINT: This will be much easier to accomplish with repetition through function invocation than with iteration.